The present invention is in electrode processing and, more specifally, a process for recoating an electrode structure for an electrolysis cell and, in particular, for a chlor-alkali electrolysis cell by the diaphragm or membrane cell process with electrodes.
The process known as direct recoating of electrodes and, in particular, that for the chlor-alkali diaphragm process, uses a complex electrode structure consisting of a mesh welded to a substructure containing a Cu--Ti rod and involves recoating the electrode without disassembly during the process. The life of an electrocatalytic recoating is limited by electrochemical, chemical and mechanical wear of the coatings. The average lifetime of a coating can be 15 years. After this period, the coating must be renewed. The classical method for recoating is either to: a) detach the mesh, or b) attempt to thermally insulate the temperature-sensitive sections such as Cu--Ti rod Ni--Ti joints. The drawback with the former is the high cost involved and in the latter the insufficient protection for the temperature-sensitive sections especially in view of the repeated temperature cycles needed to obtain the desired coating thicknesses.
The current practice for the recoating of electrodes generally involves the repeated application of a coating solution to the electrodes followed by furnacing between each coating operation. This process is satisfactory if the electrodes are made exclusively of a single metal, usually titanium. If, however, the electrode or its components are made from one or more metals, the resulting temperature variations can induce stresses at the interfaces between the dissmilar metals within the rod. The developing stresses can be of a sufficient magnitude to cause disruption of the bonds between the metals resulting in delamination. Such a delamination adversely effects the performance of the recoated electrode structure.